Mike Singletary spun the revolving door again Tuesday. The 49ers coach announced that Alex Smith will start at quarterback Sunday against Seattle because “right now he gives us the best chance to win.”

That’s wrong, of course. Drew Brees or Tom Brady would give the 49ers a far better chance to win. But neither is on their roster. It has been the basic problem all along.

And so we get the revolving door that contains Alex Smith and the unrelated Troy Smith, who has been the starter since Alex dislocated his non-throwing shoulder more than six weeks ago.

But don’t cringe. It makes sense that Alex will be back behind center for the win-or-be-eliminated game against the Seahawks. In a strange way, I’m looking forward to it.

For one thing, during Alex Smith’s six seasons as a pro, he has faced the Seahawks more times than he has faced any other team. He knows their personnel, their schemes. He has had just two 300-yard games in the NFL. One was against the Seahawks, last year. In defeat, of course. But still.

For another thing, you may have noticed that Troy Smith continued his dysfunctional pattern Sunday in the loss at Green Bay. Troy has a fantastic ability to throw long touchdown passes and a spectacular inability to convert short ones when needed. The 49ers were just 18 for 61 on third-down conversions in the five games Troy started.

Best and most importantly, however, the choice to restart Alex sets up a terrific drama-within-the-drama for Sunday afternoon.

Because this is Alex Smith’s last stand. His final showdown with the rest of his football life. After being given so many second chances, this is going to be Smith’s ultimate, conclusive test.

Not just as a 49ers starter. But as an NFL quarterback. Period.

If Smith is effective Sunday and the 49ers win to stay mathematically alive for the playoffs, he remains a viable pro. The 49ers might or might not keep him around another season — he is an unrestricted free agent for 2011 — but a respectable performance against Seattle in an elimination game certainly would convince another franchise that Alex is worth taking a flier on as a potential backup or maybe even as a starter. He is only 26 years old.

On the flip side, if Smith is lousy Sunday and loses, he basically is done as a pro with a future. The 49ers definitely would drop him after the season. And no other NFL team would give a thought to putting Smith on a roster as anything other than a No. 3 quarterback. He would be JaMarcus Russell without the sippin’ syrup. Smith might be reduced to scuffling about in the United Football League or an analyst for Big Sky Conference games.

As reality television goes, that should be pretty riveting. A man’s career on the line? With fans ready to savage him? And blitzing linebackers seeking violence against him? It will be a little more gritty than anything on “Keeping Up With The Kardashians.”

Anyone who has been around Alex Smith during his time with the 49ers knows he is a fine guy. His charity work is sincere and generous. He is smart. He studies and prepares diligently. If the NFL were an SAT test, he would be in the Super Bowl every year. But his won-lost record in actual football games is 17-30. It’s the grade card that matters.

Yes, the 49ers mishandled him. They threw him into action too soon. They kept changing offensive coordinators. There will be an eternal argument about whether Smith could have become a top-tier NFL quarterback under different circumstances. Fans of the 49ers will debate that question the same way that fans of the Golden State Warriors debate how the franchise might have prospered if the team had drafted Kobe Bryant in 1996 rather than Todd Fuller.

Both debates are useless and counterproductive. Because in both cases, there’s no way to ever know the answer. In sports, the only answers that matter are the ones still in play, the ones still in the air.

For the 49ers, Sunday afternoon is win or be done for 2010. For their starting quarterback, it’s win or become an NFL afterthought. Other than that, nothing much else is at stake for Alex Smith.

Mark Purdy is a sports columnist for the Bay Area News Group. He joined the organization's Mercury News in 1984 and has covered 14 Olympic Games, more than 30 Super Bowls and more than 20 World Series. He concentrates mostly on the Bay Area's professional teams but covers all sports. He was there for the first Sharks' game at the Cow Palace in 1991 and documented the team's 2016 Stanley Cup playoff run.

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